iMovie Trouble

Just this morning, I imported two clips (one is a .mpg and the other is a .mov). Then, when I go to import another clip, it finishes importing but then a message comes up saying it failed to import due to an unknown error. These clips I've tried to import have worked in the past in iMovie, and they're .mov files. So, I wanted to know why they won't import, could anyone help me out?

Can anyone tell me what the problem is?

(Sorry for double posting, but no reply still =()

Have you tried looking to see if your iMovie version has any available updates?
You can also try a permissions repair to see if that clears things up.

Nope, I just tried importing a clip, and it STILL won't go in. I even repaired the permissions (do I need to restart AFTER that, or is it fine if I don't?) Also, there aren't anymore updates, I already got the latest one. So I don't know what the problem is.

Can anyone help me? Sorry if it looks like I'm a n00b, but I'd really like to know what I can do to fix this!

Some files won't import. I asked a question like this in another thread. IRC, the person said .avi's and some .mov's and .wmv's don't work because the sound and video aren't separate (or something like that). Hopefully someone can clarify more.

I realize some won't import, but as I said in my initial post. They worked before, and I have no idea why they won't work now.